Furlable heat exchanger



Feb. 24, 1970 H; ROSEN ETAL FURLABLE HEAT'EXCHANGER 3 Sheets-Sheet 1Filed June 23. 1967 NN EE MOT 0R8 w D mLR A N AR HE B KENNETH E.'MAYOATTORNEY Feb. 24, 1970 H.RQSEN ETAL I 3,496,995

FURLABLEHEAT EXCHANGER Filed June 23'. 1967 3 Sheets-Sheet 2 INVENTORSHAROLD ROSEN BERNARD STEIN KENNETH E. MAYO ATTORNEY Feb. 24, 1970 H.ROSEN 3,496,995

FURLABLE HEAT EXCHANGER Filed June 23, 1967 3 Sheets-Sheet 3 HAROLDROSEN BERNARD STEIN FIG. 40 KENNETH E. MAYO ATTORNEY United StatesPatent 3,496,995 FURLABLE HEAT EXCHANGER Harold Rosen, Nashua, N.H.,Bernard Stein, Andover, Mass, and Kenneth E. Mayo, Nashua, N.H.,assignors to Sanders Associates, Inc., Nashua, N.H., a corporation ofDelaware Filed June 23, 1967, Ser. No. 648,294

Int. Cl. F281? /00 US. Cl. 16546 12 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND OF THE INVENTION This invention relates to thermal heatexchangers and more particularly to furlable heat exchangers which canbe packaged to occupy a small space when in an inoperative position, butwhose heat transfer surface area can be increased by unfurlingpreparatory to becoming operative. These forms of heat exchangers haveparticular application in outer space and other alien environments.

One of the major problems with space power generators utilizing thermalcycles has been the amount of radiator surface required for waste heatrejection. In transporting these generators to space environmentalregions, their on board size and weight restrictions must, of necessity,be minimal. However, since low radiator temperatures are essential tohigh efficiency of such heat exchangers, the total heat transfer surfacearea, when operative, must be rather large. Though we recognize thatheat transfer will occur from these heat exchanges by radiation orconvection, or both, we will nevertheless henceforth refer to thesesurfaces as radiators. Of course, if the heat exchangers are employed ina space vacuum, no heat exchange takes place by convection.

In order to minimize on board launch vehicle volume as power packs arecarried into space, we have discovered that a furlable radiator can befabricated which would adequately meet both the size and heat exchangerequirements. The radiators contemplated by this disclosure are packagedin a collapsed (i.e. furled) condition, and packed snugly around andintegrally connected to the heat generator system. During the launchphase of the space vehicle, in-transit cooling for this limited periodcan be provided by using the heat capacity of the associated materials;for example, the heat-sink capacity of the adjacent launch vehiclestructure and skin, and the self-contained coolant. When the high g andhigh atmospheric drag portion of the flight profile is passed, theradiator and self-contained power generator may be deployed overboardfrom the spacecraft whereupon the radiator arms are unfurled and allowedto occupy as much space as is required by the design. Depending on theheat rejection requirements, these radiator arms may extend anywherefrom a few feet in length to fifty or more feet in length. When suchradiators are employed in vacuum environments, the heat transfer willoccur through radiation; on the other hand, should the radiator3,496,995 Patented F eb. 24, 1970 ice be in a gaseous environment, heattransfer will occur by both radiation and convection.

Accordingly, it is among the various objects of this invention toprovide a heat exchanger which pres nts a large surface area for heattransfer in its operative condition, but which can be furled andpackaged into a small volume while it is inoperative.

It is a further object of this invention to provide a heat exchangerwhich is readily collapsible but which will automatically unfurl itsheat transfer portions into operative position at a predetermined time.

It is a still further object of this invention to provide a fnrlableheat exchanger wherein the heat transfer or so-called radiator surfacesare held in an extended position through the action of pressurizedcirculating coolant and the unfurlable characteristics of the structureitself.

Another object of this invention is to provide a furlable heat exchangerwhich dispenses with the need for a mechanical circulating mechanism butwhich instead utilizes a change-of-state coolant.

These and other objects will become more apparent in light of thefollowing disclosure, when taken in conjunction with the variousdrawings in which:

FIGURE 1 illustrates a self-contained power package and furlable heatexchanger with self-coiling arms;

FIGURE 2 depicts another embodiment of a furlable heat exchanger;

FIGURE 3 illustrates a still further form of a furlable heat exchangerin sequential deployment from a spacecraft;

FIGURE 3a illustrates in schematic form a typical pattern of coolantflow through one of the several heat transfer members of the heatexchanger of FIGURE 3;

FIGURE 4 illustrates a still different embodiment of a furlable heatexchanger in a sequential deployment from a spacecraft;

FIGURE 4a depicts in schematic form a typical pattern of coolant flowthrough one of the several heat transfer members of the heat exchangerof FIGURE 4; and

FIGURES 5, 5a and 5b illustrate a further embodiment of a furlable heatexchanger for use in gravitational environments.

PREFERRED EMBODIMENTS Referring now with greater particularity to FIGURE1, there is shown therein a self-contained, interconnected power package10 comprising a storage tank 11 for the storage of coolant, a pump 12and a power supply 13 whose excessive heat loads must be dissipated.Surrounding this power package in substantially coplanar form is ahollow, flexible structure comprising a generally toroidal portion 14and a plurality of radiator arms 15 flexibly, integrally connected to,and radially extending from this toroidal portion outwardly to a lengthof fifty or more feet. As seen in FIGURES 1 and 1a, each radiator 15 iscomprised of two separated channels 15a, 15b connected in serial fashionat their outer and inner ends respectively. Coolant is circulated fromstorage tank 11 through pump 12 and power supply 13 into channel 15a ofone of radiator arms 15 where it flows in serial fashion through thechannels of the remaining radiator arms and finally returns to thestorage tank in a conventional manner. As this collant flows through thearms 15, cooling by radiant heat transfer or convection or both(depending on the environmental circumstances) occurs from the surfaceof the collapsible arms which remain extended by virtue of the pressureof the coolant fluid circulating through these channels. At such time aspump 12 stops, pressure is lowered, and arms 15 will, because of springwires 19, begin to furl. This in turn will cause the coolant fluidremaining in the arms to regress into storage tank 11.

An essential concept of this invention is that in those instances wherethe heat exchanger may have alternate periods of non-use, the radiatorarms should furl automatically. In order to provide this feature, theradiator arm material can have embedded therein lengths of spring wire19 as shown in FIGURE 10. When no coolant is circulating, theself-coiling feature of wire 19 will furl radiator arms 15 as shown inthe drawing. When the device is operative however, and fluid coolant iscirculating, the coolant flow pressure will overcome the springconstantof wires 19 and unfurl radiator arms 15 to their extended form.

It is obvious that any number of coolant circulating schemes can beprovided. For example, in the embodiment of FIGURE 2 the outboard ends20 of alternate arms 21, 22 are connected to an intermediate arm 23 sothat the outboard channels receive hot coolant which flows into thisintermediate return line and exhausts into the coolant reservoir (notshown). A heat exchanger of this nature then assumes the form of aclosed polygonal geometric shape which in the case of FIGURE 2 ishexagonal.

In FIGURES 3 and 4, there is depicted in schematic view other forms ofthis invention. Referring to FIGURE 3, a furled heat exchanger 30enclosed with a cover 32 is discharged overboard from cavity storage 31in space vehicle 29. At a predetermined time thereafter, covers 32 arecast off and the heat exchanger arms 33, integrally and flexiblyconnected to cylindrical pump housing 34, are unfurled to a fullydeployed radial position. As schematically illustrated in FIGURE 3a,each of the arms 33 contains a channel 54, the inner end 54a of whichreceives coolant discharged from pump 16 carried within housing 34,while the other end of this channel 54b communicates with conventionalfluid circuitry within housing 34 for circulating the low temperaturecoolant into a reservoir and through the power package where itstemperature is raised before it is pumped outboard into the arms againfor cooling. It is to be understood that housing 34 may contain thepower package from which heat is extracted, or alternatively, this powerpackage can remain inboard of the space vehicle and have the coolantfluid connected therefrom to the pump and radiator arms.

Referring to the embodiment shown in FIGURE 4, there is schematicallyshown another form of heat exchanger 40 being discharged overboard fromcavity 41 of space vehicle 39. The heat transfer arms 42 are flexiblyconnected to one end of cylindrical housing 43 and when fully deployed,extend radially therefrom. Adjacent arms are channeled for coolantcirculation as shown in FIG- URE 4a. Each of the previously describedembodiments illustrate heat exchangers in which a liquid coolant havinga high vaporization temperature is employed and which accordinglyrequires a mechanical pumping mechanism for circulation.

In FIGURES and 5a however, there is illustrated in schematic form anunfurlable heat exchanger in which no mechanical pumping mechanism forcirculating coolant fluid is necessary, so long as gravitationalinfluences are present. The device depicted in FIGURE 5 is comprised ofa power package 50 surrounded by a fluid reservoir of coolant 51, bothcontained within a suitable housing 52 from which upwardly extend aplurality of furlable heat transfer arms 53. The arms 53 (sectionallyshown in FIG- URE 5b) consist of a single channel and are initiallyfurled into a coil. In operation, heat from the power supply causes theliquid coolant to boil and vaporize; the colant vapor, as it expands,flows into the arms and unfurls them. As this vapor cools, it condenseson the interior walls of the radiator arms as a liquid and flows backinto the reservoir where it is heated and enters into thischangeof-state cycle again. It is necessary in the design of this formof heat exchanger, however, to assure that the unfurlable arms areinclined upwardly from the coolant reservoir to permit the condensate toflow into the reservoir under gravitational influence.

The heat exchanger material of the embodiments disclosed is preferably ametallic foil (e.g. aluminum, steel, copper or the like) for readilyconducting heat energy from the circulating coolant to the surface ofthe heat transfer arms. A further characteristic which is intended inthe preferred embodiments of these heat transfer arms is that whereapplicable they be self-coiling, i.e. when there is no coolant pressureor flow, these arms should automatically furl. It may be that thematerial selected will itself exhibit this memory feature; if not, thenspringwire may be embedded into these arms to product such aself-coiling feature.

The coolant fluid may be any liquid or gas suitably appropriate for theenvironmental use; however, in the embodiment of FIGURE 5 which requiresno mechanical circulation, the coolant employed must be a liquid andthis liquid must vaporize at some temperature below that of theenvironment the heat exchanger is in, in order that the heat exchangeroperate in its intended mode. The term liquid is also intended toembrace metals, so long as they are in a fluid state when used in acoolant capacity.

Generally the major mode of heat transfer of these exchangers will occuras radiation emitted from the arms. However, when used in alienenvironments, radiant energy from solar sources may at times also beincident on the radiator surfaces and will accordingly be absorbed. Thenet rate of loss of thermal energy then is the difference between therate of emission from radiator surfaces, and the rate of absorption fromexternal sources to these surfaces. To some extent it is possible by aproper selection of spectral characteristics to control this net rate ofheat loss by controlling the range of wave lengths of energy to beemitted, as opposed to the range of wave lengths which are to beabsorbed. In order to employ these parameters to best advantage, thisinvention contemplates coating the radiator arms with any of a number ofinorganic substances to obtain a favorable absorptivity to emissivityratio. As an example, these coatings may be aluminum phosphate,potassium silicate, or sodium silicate. The coatings recited as examplesmay be pigmented to yield an optimum absorptivity to emissivity ratio inorder to radiate those wave lengths of thermal energy desired to beemitted, while at the same time providing reflectivity for those wavelengths of thermal energy which are not desired to be absorbed.

We have thus disclosed several novel forms of heat exchanges for use inenvironments alien to earth, and have accordingly achieved ourobjectives of providing an operative power package and radiator systemwhich can be easily transported through space and yet adapt itself,automatically, by change in size to operate elficiently and effectively.Though we have particularly described our invention in terms of specificradiator orientation with respect to the hub of the power package, we donot desire or intend to be thus limited. It should be obvious, now, inlight of our disclosure, that any number of various geometries of flowand radiator orientations can be provided to meet the demands of varyingcircumstances since these disclosures are merely illustrative of ourinvention.

While the invention has been described with respect to cooling, it wouldbe obvious to employ the principles in radiation heat absorptionapplications.

We claim:

1. A heat exchange system comprising: at least one heat exchange arm;means for furling said heat exchange arm; and means for unfurling saidheat exchange arm including means for circulating fluid.

2. The structure of claim 1 wherein said means for circulating fluidincludes pumping means for pumping fluid into said heat exchange armwhereby the pressure of the circulating fluid causes said heat exchangearm to unfurl.

3. The structure of claim 2 wherein said means for furling said heatexchange arm includes a spring arranged therein whereby said heatexchange arm will furl when the pressure of the circulating fluid islowered.

4. The structure of claim 3 further including a reservoir of heattransfer fluid for accommodating the fluid when said heat exchange armis in its furled condition.

5. A self-contained power package comprising: a power supply, means forcirculating fluid through said power supply, and a furlable heatexchanger including at least one furlable channel which unfurls uponapplication of circulating fluid thereto.

6. The structure of claim 5 wherein said furlable heat exchanger furtherincludes a reservoir of heat transfer fluid in communication with saidfurlable channel for accommodating the heat transfer fluid when saidchannel is in its furled condition.

7. The structure of claim 6 wherein said furlable heat exchangerincludes means for circulating the heat transfer fluid through saidchannel in its unfurled condition.

8. A heat exchange system comprising: at least one furlable radiator armand a cooling fluid whereby when said cooling fluid boils the vaporexpands causing said radiator arm to unfurl.

9. The structure of claim 8 and further including a fluid reservoirwherein said radiator arm is inclined upwardly so that said vapor uponcooling condenses and flows out of said arm into said reservoir.

10. The structure of claim 8 wherein said radiator arm is biased to afurled condition.

11. A self-contained power package comprising: a power supply, a coolantfluid in communication with said power supply, and at least one furlableradiator arm biased in a furled condition, such that when said coolantboils the vapor will expand and cause said radiator arm to unfurl.

12. The structure of claim 1 wherein at least one surface of said heatexchange arm is coated to achieve maximum net radiative heat absorptionor dissipation.

References Cited UNITED STATES PATENTS 1,714,988 5/1929 Schlaich 734182,212,128 8/1940 Richter 73418 3,382,920 5/1968 Esselman et a1. 133

ROBERT A. OLEARY, Primary Examiner CHARLES SUKALO, Assistant ExaminerUS. Cl. X.R. 16547, 86; 2441

